Tuning-fork type crystal resonator and method of frequency adjustment thereof

ABSTRACT

The invention relates to a tuning-fork type crystal resonator in which the frequency adjustment accuracy is increased, and a frequency adjustment method thereof. In a tuning-fork type crystal resonator having a tuning-fork shaped piece of quartz crystal in which a pair of tuning fork arms extend from a tuning fork base, and a frequency adjustment method thereof, there is provided a first frequency adjustment step for adjusting an oscillation frequency by forming inclined surfaces spanning from outer peripheral surfaces surrounding the pair of tuning fork arms toward distal end surfaces, by using a femtosecond laser irradiated in a direction from the outer peripheral surfaces toward the distal end surfaces, or in a direction from the distal end surfaces toward the outer peripheral surfaces.

TECHNICAL FIELD

The present invention relates to a tuning-fork type crystal resonator(referred to hereunder as a “tuning-fork type resonator”) and a methodof adjustment of the oscillation frequency thereof. In particular, itrelates to a method of frequency adjustment of a tuning-fork typeresonator in which the adjustment accuracy is increased.

BACKGROUND ART

1. Background of the Invention

Tuning-fork type resonators are especially used as reference sources forclocks, and are built into not only watches but also electronicequipment such as portable telephones, digital cameras, and the like asparts providing a clock function. In recent years, as such electronicequipment has become widespread and small sized, tuning-fork typeresonators have also been formed by etching using photolithography.

2. Prior Art

FIG. 4 is a plan view of an example of a conventional tuning-fork typeresonator, viewed with its lid removed. Furthermore, FIG. 5A and FIG. 5Bare diagrams of the tuning-fork type resonator described in detail. Inparticular, FIG. 5A is a perspective view of the tuning-fork typeresonator, including the electrode wiring, and FIG. 5B is across-sectional diagram showing a cross-section through line A-A of FIG.5A with an oscillator circuit.

As shown in FIG. 4, the example of a conventional tuning-fork typeresonator is provided with a tuning fork shaped quartz crystal piece 3with a pair of tuning fork arms 2 a and 2 b extending from a tuning forkbase 1. The two tuning fork arms 2 a and 2 b have excitation electrodes4 on each of their four surfaces excluding the distal end surfaces (headsurfaces). As shown in FIG. 5B, all of the excitation electrodes 4 areconnected. That is, they are connected such that the electric potentialsbetween each of the two main surfaces and between each of the two sidesurfaces in the respective tuning fork arms 2 a and 2 b are the same,those between the two side surfaces and the two main surfaces arereversed, and the electric potentials between the two main surfaces andbetween the two side surfaces of the tuning fork arms 2 a and 2 b arereversed relative to each other.

Excitation electrodes 4 with the same potentials are connected together,and as shown in FIG. 5A, a pair of electrodes extends to the bottom ofthe main surfaces of the tuning fork base 1. Normally, as shown in FIG.4, metal films 5 a and 5 b for frequency adjustment are formed on themain surfaces on the tip sides of the tuning fork arms 2 a and 2 b. Thenthese, including the excitation electrodes 4 and the like are outlinemachined by etching using photolithography, for example, and many tuningfork shaped quartz crystal pieces 3 are connected integrally on a quartzcrystal wafer 9 as shown in FIG. 2, which is described later.

After being divided into individual tuning-fork shaped quartz crystalpieces from the quartz crystal wafer 9 as shown in FIG. 2, the bottom ofthe main surface of the tuning fork base 1 of a tuning-fork shapedquartz crystal piece 3 is fixed to inner wall pad sections 7 at one endof a surface mount housing (enclosure) 6 having a concave cross-section,which provides terminals to the quartz crystal, and is connectedelectrically and mechanically. The open end surface of the surface mounthousing (enclosure) 6 is sealed by a lid (not shown in the figure), andthe tuning-fork shaped quartz crystal piece 3 is sealed in. Normally,this is a vacuum seal, which limits the increase in crystal impedance(CI) caused by miniaturization.

With this device, in a state in which the tuning-fork shaped quartzcrystal pieces 3 are connected integrally on the quartz crystal wafer 9,parts of the metal films 5 a and 5 b on the main surfaces of the tipsare removed by melting and dispersing using a laser such as a YAG or thelike. Then, the oscillation frequencies of the tuning-fork typeresonators (tuning-fork shaped quartz crystal pieces 3) are adjustedfrom low to high. In this case, since the frequency of the tuning-forktype resonators can be adjusted at a quartz crystal wafer levelcollectively, it is possible to increase the productivity.

Alternatively, the frequency of the tuning-fork type resonator may beadjusted by removing parts of the metal films 5 a and 5 b, similarly,after the tuning-fork shaped quartz crystal piece 3 is housed in thesurface mount housing (enclosure) 6. In this case, the oscillationfrequency at room temperature can be adjusted within the specificationallowing for the change in the oscillation frequency when the tuningfork base 1 is fixed on the pad sections 7. Furthermore, it is alsopossible to adjust the oscillation frequency finely after adjusting theoscillation frequency of each of the tuning-fork shaped crystal pieces 3roughly in a quartz crystal wafer 9 state, and separating them intoindividual pieces to be housed in the surface mount housings(enclosures) 6.

Moreover, there is another method in which characteristic adjustment isperformed by gradually cutting off the outer corners of the oscillationarm parts of the tuning-fork type quartz crystal piece using a laserlight with a wavelength suitable for cutting quartz crystal.

(Refer to Japanese Unexamined Patent Publication No. 2004-201105,Japanese Unexamined Patent Publication No. 2004-289237, JapaneseUnexamined Patent Publication No. 2007-57411, and Japanese UnexaminedPatent Publication No. 2000-278066)

Problems in the Prior Art

However, in the conventional tuning-fork type resonator with theabove-described construction, since the metal films 5 a and 5 b forfrequency adjustment need to be formed at the tips of the tuning forkarms 2 a and 2 b, the manufacturing process becomes complicated. At thetime of frequency adjustment, since the metal films 5 a and 5 b areremoved by the heat of a laser, the temperature of the tuning fork arms2 a and 2 b themselves (tuning-fork type resonator itself) alsoincreases. The frequency-temperature characteristics of a tuning-forktype resonator follow a quadratic function with the maximum being in thevicinity of room temperature.

Therefore, even if the frequency of the tuning-fork type resonator isadjusted at room temperature, the frequency adjustment is actuallyperformed at a higher temperature than room temperature due to theincrease in the temperature of the tuning fork arms 2 a and 2 b. As aresult, the frequency adjustment is inadequate, so there is a problem inthat the adjustment accuracy is likely to fall.

FIG. 6 is a diagram to demonstrate the problem, and is a diagram showinga typical example of the frequency-temperature characteristics of atuning-fork type resonator. It shows a diagram of thefrequency-temperature characteristics of a tuning-fork type resonatorwith the horizontal axis being temperature, and the vertical axis beingthe frequency variation amount (units: ppm) with respect to roomtemperature at each temperature.

A tuning-fork type resonator is normally designed such that the peak isin the vicinity of a temperature of 25° C. (the temperature coefficientbecomes flat). Furthermore, the frequency adjustment accuracy isrequired to be within ±20 ppm. However, as described above, in the casewhere the metal film is removed by the heat of a laser, at the time oflaser irradiation the quartz crystal reaches a considerable temperature(at least 100° C. or greater). Therefore, since the frequency variationbecomes a value in the region at 100° C. or greater in FIG. 6, itbecomes several 100 ppm lower than that at room temperature.Accordingly, when the laser adjustment is completed, and the quartzcrystal cools down, the frequency shifts upwards. As a result, thefrequency at the time of frequency adjustment cannot be maintained, sothat the specified frequency adjustment accuracy cannot be ensured.

Moreover, as another problem, the frequency adjustment range is limitedby the thickness of the metal films 5 a and 5 b. That is, since a YAGlaser can only remove the metal films, then after removing the metalfilms, the frequency of the quartz crystal oscillator cannot beadjusted. Accordingly, there is a natural limit to the frequencyadjustment range. Therefore, it is necessary to reduce the frequencydistribution after the external appearance of the tuning fork is formedusing photolithography, and as a result, there are considerablemanufacturing restrictions.

Objects of the Invention

The present invention has objects of providing a tuning-fork typecrystal resonator in which the frequency adjustment accuracy isincreased, and a method of frequency adjustment thereof.

DISCLOSURE OF THE INVENTION

The present invention is a method of frequency adjustment of atuning-fork type crystal resonator having a tuning-fork shaped piece ofquartz crystal in which a pair of tuning fork arms extend from a tuningfork base, comprising a first frequency adjustment step for adjusting anoscillation frequency by forming inclined surfaces spanning from outerperipheral surfaces surrounding the pair of tuning fork arms towarddistal end surfaces, by using a femtosecond laser irradiating in adirection from the outer peripheral surfaces toward the distal endsurfaces, or in a direction from the distal end surfaces toward theouter peripheral surfaces.

Effects of the Invention

Using such a construction, since a femtosecond laser [ultrashort pulselaser: 1 femtosecond (10⁻¹⁵ seconds)] is used, it is possible to cut offthe tip surfaces of the pair of tuning fork arms directly. Accordingly,frequency adjustment is theoretically possible provided the quartzcrystal itself can be cut, so that the frequency adjustment range can bewidened compared with the case of removing a metal film. Moreover, sincea metal film does not need to be used for frequency adjustment, themetal film [typically a gold (Au) film] conventionally required isunnecessary, so that it is also possible to eliminate a metal filmforming process and reduce the metal material cost. Furthermore using afemtosecond laser (ultrashort pulse laser) has little thermal impact ona piece of quartz crystal, so that effectively no temperature increaseoccurs at the time of frequency adjustment. That is to say, in afemtosecond laser, the laser pulse width is so narrow that laserirradiation ends before heat transfer to the periphery of the laserirradiation position occurs. Therefore a temperature increase at thetime of frequency adjustment of the tuning fork shaped quartz crystalpiece can be prevented. As a result, the accuracy of the frequencyadjustment of the tuning-fork type resonator can be further increased.

Moreover, since a femtosecond laser is irradiated from the outerperipheral side surfaces of a pair of tuning fork arms to the distal endsurfaces or from the distal end surfaces to the outer peripheral sidesurfaces, at the time of irradiation, the femtosecond laser permeatesthe tuning fork arms in a diagonal direction. Therefore, energy due tothe femtosecond laser is not confined inside of the quartz crystalpiece, so that it is possible to prevent or reduce cracking of thequartz crystal piece.

In contrast, in the case where a femtosecond laser is incident on themain surfaces of the tuning fork arms vertically, the energy of thefemtosecond laser is likely to be confined inside of the quartz crystalpiece, which causes cracking in the quartz crystal, and damages theinside of the quartz crystal.

In the present invention, the outer peripheral surface is the mainsurface of the tuning fork arm. As a result, it is possible to adjustthe frequency easily with the tuning-fork shaped quartz crystal pieces 3in a quartz crystal wafer 6 state or after each of the tuning-forkshaped quartz crystal pieces 3 is housed in the surface mount housing(enclosure) 6 having a concave cross-section.

Furthermore, in the present invention, an oscillation frequency isadjusted in a state in which the tuning-fork shaped quartz crystalpieces are outline machined using etching, and they are connectedintegrally on a quartz crystal wafer. As a result, frequency adjustmentis performed collectively at the quartz crystal wafer level, which makesthe adjustment efficient.

Moreover, in the present invention, the tuning-fork shaped quartzcrystal piece has an adjustment metal film on a main surface on a tipside of the tuning fork arm, and there is provided a second frequencyadjustment step for removing part of the adjustment metal film using alaser, after the first frequency adjustment step using the femtosecondlaser.

This enables highly accurate frequency adjustment of a crystaloscillator by performing frequency adjustment of the tuning-fork typeresonator by rough adjustment in the first frequency adjustment and fineadjustment in the second frequency adjustment.

Furthermore, in the present invention, the first frequency adjustmentstep is executed in a state in which the tuning-fork shaped quartzcrystal pieces are connected integrally on a quartz crystal wafer, andthe second frequency adjustment step is executed in a state in whichthey are each housed in a surface mount housing (enclosure) having aconcave cross-section. As a result, since rough adjustment in the firstfrequency adjustment step can be performed in a quartz crystal waferstate collectively, the frequency adjustment becomes efficient.

Moreover, in the present invention, the laser used in the secondfrequency adjustment step is a femtosecond laser with lower power thanthe laser power of the first frequency adjustment step. As a result, thelaser equipment in the first frequency adjustment step can be used inthe second frequency adjustment step, and fine adjustment can beperformed with a lower heating effect.

In the present invention, the first frequency adjustment step irradiatesthe femtosecond laser continuously while executing frequency measurementof the tuning-fork shaped piece of quartz crystal (that is to say, whilemeasuring the frequency with a frequency measuring probe contactedagainst the tuning-fork shaped piece of quartz crystal). The reason fordoing it this way is in order to positively utilize the characteristicsof the femtosecond laser, in that with the femtosecond laser, the laserpulse width is so narrow that laser irradiation ends before heattransfer occurs. By measuring the frequency while irradiating thefemtosecond laser continuously, frequency measurement is performedmoment by moment. Therefore, frequency adjustment accuracy can beincreased compared to the conventional case of using the YAG laser.

Furthermore, in the present invention, an incident angle with respect toa main surface of the tuning fork, of the femtosecond laser that formsthe inclined surfaces is 30 to 70°. In a case where the femtosecondlaser is vertically incident, the laser light shines into the interiorof the quartz crystal. If this happens, laser damage is likely to occur.With inclined irradiation, the laser light can easily cut the sidesurface, but is unlikely to shine into the interior of the quartzcrystal, and hence damage to the interior of the quartz crystal can beprevented.

In the second frequency adjustment step, a construction is described inwhich a metal film is removed. However, the arrangement may be such thatadjustment is performed by cutting the quartz crystal using afemtosecond laser light with lower power than the power at the time ofthe first frequency adjustment step.

Here the pulse width of the femtosecond laser used in the presentinvention is preferably less than or equal to 500 fs (femtoseconds),more preferably less than or equal to 200 fs, and further preferablyless than or equal to 100 fs. The shorter the pulse width, the moresignificant the effect of using the femtosecond laser, and thermaldamage can be reduced. Furthermore, the effect of the present inventioncan be obtained with the power of the femtosecond laser being severalμJ/pulse to several 10 μJ/pulse. Moreover, since the femtosecond laseris a pulsed laser, the pulse repetition frequency is also an importantparameter. The pulse repetition frequency may be several 100 Hz,preferably 500 Hz or more, and more preferably 1000 Hz or more. With ahigher pulse repetition frequency of the femtosecond laser, the numberof irradiation pulses per unit time can be increased making it possibleto shorten the time for frequency adjustment.

Furthermore, in the present invention, the femtosecond laser isirradiated diagonally from the outer peripheral surface surrounding thetuning fork arms toward the distal end surfaces, or from the distal endsurfaces toward the outer peripheral surfaces, in order to form inclinedsurfaces extending from the tuning fork outer peripheral surface to thedistal end surfaces. The angle of diagonal irradiation (incident anglewith respect to the tuning fork main surfaces) is preferably 30° to 70°,more preferably 40° to 70°, and further preferably 45° to 60°, but isnot limited to this.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a frequency adjustment step of atuning-fork type resonator of the present invention, wherein FIG. 1A isa front view of a tuning-fork shaped quartz crystal piece 3, and FIG. 1Bis an enlarged cross-sectional diagram of a part thereof.

FIG. 2 is a diagram showing an embodiment of a method of frequencyadjustment of the tuning-fork type resonator of the present invention,and is a front view of a quartz crystal wafer on which tuning-forkshaped quartz crystal pieces 3 are assembled integrally.

FIG. 3 is a diagram showing an embodiment of the method of frequencyadjustment of the tuning-fork type resonator of the present invention,and is a plan view of the tuning-fork type resonator viewed with its lidremoved.

FIG. 4 is a plan view of an example of a conventional tuning-fork typeresonator viewed with its lid removed.

FIG. 5 shows the tuning-fork type resonator in detail, wherein FIG. 5Ais a perspective view thereof with electrode wiring added, and FIG. 5Bis a cross-sectional diagram through line A-A of FIG. 5A.

FIG. 6 is a diagram showing a typical example of thefrequency-temperature characteristics of a tuning-fork type resonator.

FIG. 7A is a block diagram showing an outline of an experimentalapparatus 100 used in the present invention. FIG. 7B is a schematicdiagram showing the arrangement of frequency measurement for a wafer.FIG. 7C is a schematic diagram showing the arrangement of probing withrespect to the tuning-fork type resonator.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 to FIG. 3 are diagrams showing frequency adjustment steps of atuning-fork type resonator according to an embodiment of the presentinvention. FIG. 1A is a front view of a tuning-fork shaped quartzcrystal piece 3. FIG. 1B is a partially enlarged cross-sectionaldiagram. FIG. 2 is a front view, where some of the quartz crystal piecesare omitted, of a quartz crystal wafer on which the tuning-fork shapedquartz crystal pieces 3 are integrated. FIG. 3 is a plan view of thetuning-fork type resonator with its lid removed.

As shown in FIG. 1A, a tuning-fork type resonator of the presentinvention is provided with a tuning-fork shaped quartz crystal piece 3with a pair of tuning fork arms 2 a and 2 b extending from a tuning forkbase 1. The tuning fork arms 2 a and 2 b have excitation electrodes 4 oneach of their four surfaces excluding the distal end surfaces, and areconnected such that the electric potentials between each of the two mainsurfaces and between each of the two side surfaces in the respectivetuning fork arms 2 a and 2 b are the same, those between the two sidesurfaces and the two main surfaces are reversed, and the electricpotentials between the two main surfaces and between the two sidesurfaces of the tuning fork arms 2 a and 2 b are reversed relative toeach other.

Excitation electrodes 4 with the same electric potentials are connectedtogether, and a pair of electrodes extends to the bottom of the mainsurfaces of the tuning fork base 1. The metal films 5 a and 5 b forfrequency adjustment are formed on the main surfaces on the tip sides ofthe tuning fork arms 2 a and 2 b. The metal films 5 a and 5 b here areformed lower than those of the conventional example, and exposedsubstrate sections 8 a and 8 b are provided above the main surfaces onthe tip side. These, including the excitation electrodes 4 and the like,are outline machined using photolithography, for example, and manytuning-fork shaped quartz crystal pieces 3 are connected with the quartzcrystal wafer 9 integrally and collectively (refer to FIG. 2). The metalfilms 5 a and 5 b may be extended to the tips of the tuning fork arms 2a and 2 b.

A method of frequency adjustment of a tuning-fork type resonator of thepresent invention comprises a first frequency adjustment step and asecond frequency adjustment step. Firstly, in the first frequencyadjustment step, a femtosecond laser (ultrashort pulse laser) Pf isirradiated from the two main surfaces on the tip side, which are theexposed substrate sections 8 a and 8 b of the tuning fork arms 2 a and 2b of each of the tuning-fork shaped quartz crystal pieces 3, toward thedistal end surfaces (head surfaces), or from the distal end surfaces tothe two main surfaces on the tip side in a quartz crystal wafer 9 state(see FIG. 2). As a result, inclined surfaces extending from the two sidesurfaces on the tip side of the tuning fork arms 2 a and 2 b, which areabove the metal films 5 a and 5 b, to the distal end surfaces are formedfor rough adjustment of the oscillation frequency.

In this experiment, a quartz crystal wafer with a thickness of 120 μmwas used. Furthermore, the irradiation conditions of the femtosecondlaser were that the pulse width was approximately 70 fs, the power was30 μJ/pulse, and the pulse repetition frequency was 1000 Hz. Needless tosay, this is just an example. Moreover, an experimental apparatus wasused with the construction described below using FIG. 7A to FIG. 7C.FIG. 7A is a block diagram showing an outline of an experimentalapparatus 100. FIG. 7B is a schematic diagram showing the arrangement offrequency measurement for a wafer. FIG. 7C is a diagram showing thearrangement of probing with respect to the tuning-fork type resonator.

The experimental apparatus 100 as shown in FIG. 7A and FIG. 7B, isprovided with a femtosecond laser optical source 101, a galvanic mirror103, an XYZ stage 105, an oscillation circuit 107 having a probe pin 107a, a frequency measuring instrument 109, and a control unit 111.

The light source 101 emits a desired femtosecond laser beam. Thegalvanic mirror 103 scans the femtosecond laser light onto the tips ofthe arm parts of the tuning-fork type resonator as specified to cut thequartz crystal. Furthermore, the construction is such that an f_(θ) lens103 a is provided on the front of the galvanic mirror 103 to adjust thefocus of the femtosecond laser beam. The XYZ stage 105 can hold thequartz crystal wafer 9, and can move the quartz crystal wafer 9 in theX, Y, and Z directions arbitrarily. The oscillation circuit 107 probesthe tuning-fork shaped quartz crystal pieces 3 on the quartz crystalwafer 9 sequentially, causing each tuning fork piece to oscillate, andit also transmits the frequency signals of the tuning fork pieces to thefrequency measuring instrument 109. The oscillation circuit 107 isconstructed such that it can move upward and downward in the Z directionwith respect to the wafer. The frequency measuring instrument 109 readsthe frequency of the tuning fork pieces via a signal of the oscillationcircuit 107. The control unit 111 controls each of the above-describedelements 103 to 109. When executing frequency adjustment, preferably thefemtosecond laser is irradiated continuously while oscillating thecrystal with the oscillation circuit, and while executing frequencymeasurement, and frequency adjustment of the tuning forks is preferablyperformed while confirming that the frequency is within the targetrange.

Needless to say, the construction of the experimental apparatus 100 isjust an example. In the case of the experimental apparatus at this time,the laser beam was scanned using a galvanic mirror. However, thearrangement may be such that the beam is only passed through anobjective lens, no scanning being performed, the XYZ stage is jogged,and the quartz crystal wafer is processed using the laser beam.

Moreover, in this experiment, laser irradiation of the front and back ofthe quartz crystal wafer 9 was performed by an experimenter reversingthe quartz crystal wafer.

In this experiment, exposed substrate sections 8 a and 8 b were providedon the tuning-fork shaped quartz crystal pieces 3. The exposed substratesections 8 a and 8 b are not essential. However, since this experimentproved that the laser beam machining was easier (cutting the quartzcrystal was easier) in the case where the exposed substrate sections 8 aand 8 b were provided and the femtosecond laser was irradiated on them,it is preferable to provide the exposed substrate sections 8 a and 8 b,and irradiate the femtosecond laser on them.

Next, in the second frequency adjustment step, as described above, eachof the tuning-fork shaped quartz crystal pieces 3 is separated from thequartz crystal wafer 9, and the tuning-fork shaped quartz crystal pieces3 are housed in a surface mount housing (enclosure) 6. The tuning forkbase 1 of each tuning-fork shaped quartz crystal piece 3 is fixed to theinner wall pad sections 7 of the surface mount housing (enclosure) 6. Inthis embodiment, similarly to the first frequency adjustment step, themetal films 5 a and 5 b on the tips of the main surfaces of the tuningforks are removed on each of the tuning-fork shaped quartz crystalpieces 3 using a femtosecond laser for fine adjustment of theoscillation frequencies of the tuning-fork type resonators.

According to such a method of frequency adjustment, since the frequencyis adjusted roughly in the first frequency adjustment step using afemtosecond laser Pf, there is no temperature increase at the time ofthe frequency adjustment, so that adjustment is possible within thespecification at room temperature. In this case, the amount of frequencyadjustment in the rough adjustment is generally several thousands toseveral tens of thousands of ppm, which is high. However, since theadjustment is by a femtosecond laser, the adjustment is performed in astate in which there is no substantial temperature effect, so that thedeviation (amount out of specification) from the specification can beminimized.

Since the adjustment of the oscillation frequency of a tuning-fork typeresonator of the present invention is performed in a state in which thetuning-fork shaped quartz crystal pieces 3 are connected on the quartzcrystal wafer 9, it is easy to ensure the locational accuracy, thelevelness of the processed part, and the like, of each tuning-forkshaped quartz crystal piece 3, which makes for excellent workefficiency. Moreover, in the present invention, since the cutting isperformed from the two main surface sides of the tuning fork arms 2 aand 2 b, it is possible to maintain the symmetrical property of thetuning-fork shaped quartz crystal piece 3, and thus maintain excellenttuning fork oscillation. Furthermore, compared with the case where thecutting is performed from one surface of the tuning-fork shaped quartzcrystal piece 3, it is possible to increase the amount cut off thequartz crystal. As a result, the frequency adjustment range can bewidened, and the amount of frequency variation per machining time can beincreased. That is, the machining time can be shortened.

Moreover, since the tuning fork arms are cut by irradiating thefemtosecond laser (ultrashort pulse laser) Pf diagonally with respect tothe main surfaces of the tuning fork arms, the femtosecond laser Pfpermeates the tuning fork arms, so there is no damage due to the laserenergy.

Furthermore, since the separated tuning-fork shaped quartz crystalpieces 3 are housed in the surface mount housing (enclosure) 6 after thefirst frequency adjustment step (rough adjustment), and fine adjustmentis performed in the second frequency adjustment step, it is possible toreduce the frequency adjustment amount at the time of the fineadjustment. The adjustment amount in this case is several tens toseveral hundreds of ppm for example. Even if the adjustment amount islarge, since a femtosecond laser is used, the amount of heat generatedby the laser Pf becomes small, so that the oscillation frequency can beadjusted within the specification at room temperature.

In the above-described embodiment of the present invention, thefemtosecond laser is irradiated from the two main surface sides of thetuning fork arms 2 a and 2 b in the first frequency adjustment step.However, the femtosecond laser may be irradiated from only one mainsurface side of the tuning fork arms 2 a and 2 b. In this case, it ispossible to simplify the construction arrangement and the like of thefemtosecond laser apparatus. Moreover, the metal films 5 a and 5 b areremoved using the femtosecond laser in the second frequency adjustmentstep. However, instead of the metal films 5 a and 5 b, the quartzcrystal itself may be cut. As a result, it is possible to omit theprocess of forming the metal films 5 a and 5 b on the tips of the tuningfork.

Furthermore, in the present invention, the tuning fork arms 2 a and 2 bare cut from the two main surface sides in the first frequencyadjustment step using the femtosecond laser. However, they may be cutfrom the side surface sides of the tuning fork arms. Essentially,provided the inclined surfaces are formed spanning from the outerperipheral surfaces surrounding the tuning fork arms 2 a and 2 b to thedistal end surfaces, a similar effect is shown. The second frequencyadjustment step may be performed using a YAG laser or the like similarlyto a conventional one, or furthermore, may be performed using an ionmilling process.

INDUSTRIAL APPLICABILITY

The method of frequency adjustment of a tuning-fork type crystaloscillator of the present invention can be widely used for frequencyadjustment of other types of crystal oscillators.

1. A method of frequency adjustment of a tuning-fork type crystalresonator having a tuning-fork shaped piece of quartz crystal in which apair of tuning fork arms extend from a tuning fork base, comprising afirst frequency adjustment step for adjusting an oscillation frequencyby forming inclined surfaces spanning from outer peripheral surfacessurrounding said pair of tuning fork arms toward distal end surfaces, byusing a femtosecond laser irradiated in a direction from said outerperipheral surfaces toward said distal end surfaces, or in a directionfrom said distal end surfaces toward said outer peripheral surfaces,wherein said tuning-fork shaped quartz crystal piece has an adjustmentmetal film on a main surface on a tip side of said tuning fork arm, andthere is provided a second frequency adjustment step for removing partof said adjustment metal film using a laser, after said first frequencyadjustment step using said femtosecond laser, wherein the laser used insaid second frequency adjustment step is a femtosecond laser with lowerpower than the laser power of said first frequency adjustment step.
 2. Amethod of frequency adjustment of a tuning-fork type crystal resonatorhaving a tuning-fork shaped piece of quartz crystal in which a pair oftuning fork arms extend from a tuning fork base, comprising a firstfrequency adjustment step for adjusting an oscillation frequency byforming inclined surfaces spanning from outer peripheral surfacessurrounding said pair of tuning fork arms toward distal end surfaces, byusing a femtosecond laser irradiated in a direction from said outerperipheral surfaces toward said distal end surfaces, or in a directionfrom said distal end surfaces toward said outer peripheral surfaces,wherein said tuning-fork shaped quartz crystal piece has an adjustmentmetal film on a main surface on a tip side of said tuning fork arm, andthere is provided a second frequency adjustment step for removing partof said adjustment metal film using a laser, after said first frequencyadjustment step using said femtosecond laser, wherein said secondfrequency adjustment step is performed by removing a metal film formedbeforehand on the tips of the tuning fork, by iron milling.
 3. A methodof frequency adjustment of a tuning-fork type crystal resonator having atuning-fork shaped piece of quartz crystal in which a pair of tuningfork arms extend from a tuning fork base, comprising a first frequencyadjustment step for adjusting an oscillation frequency by forminginclined surfaces spanning from outer peripheral surfaces surroundingsaid pair of tuning fork arms toward distal end surfaces, by using afemtosecond laser irradiated in a direction from said outer peripheralsurfaces toward said distal end surfaces, or in a direction from saiddistal end surfaces toward said outer peripheral surfaces, wherein saidfirst frequency adjustment step irradiates said femtosecond lasercontinuously while executing frequency measurements of said tuning-forkshaped piece of quartz crystal.
 4. A method of frequency adjustment of atuning-fork type quartz crystal resonator according to claim 3, whereinan incident angle with respect to a main face of said tuning fork, ofsaid femtosecond laser that forms said inclined faces is 30 to 70°.